@useruser Well, those eggshells might be sharp when cracked... XD
Jokes aside (and ignoring the possibility that the damage is completely unrelated to baking.. maybe she bit herself in a fit of jealous anger before deciding to cook) it might be either of:
a) She had to help with normal cooking to be allowed to borrow the kitchen for her own purposes (and cut herself while peeling or chopping in a standard manga manner).
b) She's covering not cut marks, but burn marks/blisters from having accidentally touched hot metal while baking.
(also apparently c) - some people say they have managed to cut themselves on eggshells)
Thinking that your partner doesn't love you enough because it doesn't feel jealousy is such a weak mindset. I've seen so many mangas where one member of the couple gets mad or decides to cheat because the other is not the jealous type; is even worse that there is people out there that think like these too; like have you heard of trust and maturity LMAO